Method of rating and comparing quantities



July 23, '1935. s. E. LEONARD, JR 2,008,832

METHOD OF RATING AND COMPARING QUANTITIES Fild June 26, 195s 5 sheets-sheet l1 .SCi//a/or WWF/1M' MMM ATORNEY.

July 23, 1935. ,s E L EQNARD9 JR 2,008,832

METHOD OF RATING AD COMPARING QUANTITIES Filed June 2e, 195s f S Sheng-sheet 2 F'lg. 4.

A TTORNE Y.

July 23, 1935. s. E. LEONARD, JR

METHOD OF RATING AND COMPARING QUANTITIES Filed June 26, 1933 5 Sheets-Sheet 5 INVENTOR.

A TTORNEY.

July 23, 1935. s. E. LEONARD. JR 2,008,832

' METHOD OF RATING AND COMPARING QUANTITIES Filed June 26, 1933 5 Sheets-Sheet 4 INVENTOR.

:PMK um. M

A TTORNE Y.

`Iuly 23, 1935. s, E, LEONARD, JR 2,098,832

METHOD wOF RATING AND COMPARING QUANTITIES ,.f /ea Fry 13 m" fr] CN l T .A w A :w to* C Y f 155 9 l9|` f o q 1 Il D l a o@ lea l l 85 /90 89 INVENToR. 'M Fly-11 3^ BY v , l (4m. HMM

A TTORNEY.

Patented July 23, 1935 A UNITED STAT-Es METHOD or RATING AND coMPAaING..

QUANTITIES Samuel Leonard, Jr., East Cleveland, Ohio Application June 26, 1933, Serial No. 677,753

1a claims'.

. This invention relates to a method of rating and comparing spatio-temperal quantities, such as altitudes and is applicable for air craft work, topv ographical Work, barometric measurements,

gage work for rating or comparing materials and liquids etc. The principal object of the present invention isto-prvide a method and means for automatically rating quantities such as altitudes in frequencies of electric oscillating circuits, by comparing frequencies governed by one altitude with other frequencies governed by another altitude for determining the relative or real altitudes. As known the frequency of an electric oscillating circuit is principally governed by the ratio of the quantities, capacity, resistance and self-induction with respect to each other, therefore an automatic change of the ratio of these quantities will cause a change of the frequency br natural period of an oscillating circuit. I have found that atmospheric pressure variations can be utilized for automatically changing the frequency of an oscillating circuit and that the resulting change in the frequency of the circuit can be directly metered in altitudes, or can readily be compared (for measurement purposes) with the frequency of a remote Voscillating circuit having a predetermined frequency governed by its altitude.

Change in the period of an oscillating circuit resulting from air Apressure variations can be automatically effected according to the present invention, by the'use of .avariable condenser resembling in general an' aneroid barometer with the exception that the two o'ppositely arranged diaphragms of 'the barometer are electrically insulated from each other. Such period .change can also be obtained by coupling an aneroid barometer or a battery thereof with'conventional variablecondensers, or by means of specifically built vacuum tubes embodying means for automatically changing their inner electrode capacity.

Tubes of this type are described in my copendingl application Serial No. 677,752 led June 26, 1933. It is obvious that oscillating circuits for metering barometric pressures or altitudes may oscillate in radio, audio or beatfrequencies.'

The above and other novel features of my inquency of these oscillations with the frequency- (Cl. Z-1) of a local oscillating circuit. 'I'he V oscillant-rus received at the receiving station are for example, sent from an aeroplane including a. sender installation such as shown in the block -diagram of Figure '2, which installation transmits electric oscillations of a frequency proportionate to the heightof the aeroplane above ground.

Figures 3 and 4 show block diagrams of receiving and sending stations of somewhat simplied construction;

Figure 5 shows a diagrammatic wiring diagram of an installation adapted to be used as the sender station of an aircraft;

Figure 6 is a diagrammatic wiring diagram of the -ground or receiver station;

Figures 7, 8 and 9 show plan, side Aand cross sectional views of a practical form' of pressure operated variable condenser installed in the sender and receiver stations referred to'above; cross sectional view 9 being taken on line 9 9 of Figure 7;

Figure 10 shows in diagram a variable condenser actuated by4 and coupled `with anv anerold barometer;

Figures. 11, 12 and 13 are plan'and crosssectional views of a calibrated dial for acalibrated condenser, the sections of Figures 12 and -13-' be ing taken on'lines I Z-IZ and. l3--I3 of Figure 11. l

In comparing and rating spatio-temperal quan-.l

.tities such as altitudes, the receiving 'fand the sending station (see block diagrams Fi-gures. l and 2) are each provided with automatically operated pressure condensers or barometer condensers. This arrangement vpermits .accurate comparison of the frequencies in all cases where the sender station,.for example an aeroplane, is relatively closely .related to'k the receiving-station so vthat the atmospheric conditions in the locality 4of the two stations are practically uniform.

'In the block diagram of the ground or receiving station'shown in Figure 1 all instruments and apparatus arel taken from standard radio equipment with the exception of barometer condenser 4, which will later be described. The apparent complication of the diagram is due to the use of frequency meters now on 'the market, these meters being designed only for oscillation Within narrow and low ranges. The two radio frequency oscillating circuits I and 2, that is,- oscillator A which includes barometric condenser 4 as a component element and oscillator C which includes calibrated condenser Il as a component element respectively, beat with ratio frequency oscillating circuit 3, that is, oscillator B, which includes 'quartz crystal 'I as a component element creating a steady constant frequency, to produce oscillations of audio frequency beat notes. Oscillations of circuit I are controlled by barometer condenser 4, whereas the oscillations of circuit 2 are controlled by a calibrated condenser or indicator II. Oscillating circuit 3 is controlled by a quartz crystal 1, which causes a constant output frequency to be sent into a low pass lter 9 for filtering out all extraneous and harmonic frequencies in order to produce a suitable pure and steady frequency" of this circuit. The filtered output of circuit 3 is fed into detectors'5 and I3 which are coupled with circuits I and 2 respectively. It will now be seen that the output of circuits I and3 mixing in detector 5 produces a beat frequency of audio range which after ame plification in amplifier Ii is fed throughwire 2Q to double pole switch D. The output frequency of circuit 2, which frequency is proportionate to the dial'setting of calibrated condenser II, is mixed in detector I3 with the output frequency of oscillating circuit 3, therefore the beat lnote of the two`mixed frequencies amplified in amplifier I4 and fed through wire 22 into detector I1 is a function of the cali- .brated dial setting of condenser -I I.

Ainto detector I1, where it mixes with the output of amplifier I4. 'Ihe resulting beat frequency is amplified in amplifier I8 and then fed into the frequency meter I9'to indicate zero beat. -This can be effected by tuning the dial of calibrated ,condenser II until zerol beat is indicated in said frequency'meter, that isuntil fthe frequencies from amplifiers I5-` and I4 are gthe same. Under these conditions the reading of the calibrate-d condenser dial 'setting will be a function of the air` pressure on barometer condenser 4. If it is desired to make the air pressure at. this level y,a basis for measurements, the -calibratedcondenser is turned to read zero beat in frequency meter I9, by means of a zero adjusting condenser of common construction, which zero adjusting condenser is arranged in the same circuit with calibrated condenser I I. It will therefore be seen that when switch D is in theposition .just described, the device can be used in the adjustment of the dial of calibrated condenser! II to the ain pressure then existing, and before measurements are taken. In other words the output of -amplifiers B and I4 are ,two different audio frequencies created by beating the' combined tuned radio frequency circuits I, and 3 and 2 and 3- respectively. Thesetwo audio frequencies arel then mixed in modulator or detector I1 to create a new audio frequency which will be the difference of the two foregoing audio frequencies.

- For measuring purposes it is necessary to throw the switch D into left hand position, Figure 1, so that the frequency output of amplifier 6 is fed through wires .20( and 23 into detector I5 and mixed with the output of receiving set I0, which is connected through wires 26. to detector I5.

'I'he beat frequency Voutput ofv detector I5, resulting from the difference of the -frequency of .the .remote station received by receiver III with an audio frequency output and the local frequency from amplifier 6, which latter is a. function of the air pressure as previously brought out, is amplified in amplifier I6 and mixed in detector I1 with the output frequency of amplifier I4. The beat note of detector I1 is amplified in amplifier I8 and indicated in the frequency meter I8 by turning the calibrated dial of condenser I I until this beat note is zero. The reading of the calibrated condenser therefore accurately indicates the difference in altitudes ofthe local station and the remote station.

The receiver I0 of the receiving station previously described picks up the signals of the remote station, for example an aeroplane, which carries a suitable arrangement of equipment, such as. diagrammatically shown in Figure 2 of the drawings. Thlis [equipment embodies an oscillating circuit 21 having as an element in this circuit barometer condenser 28 and an oscillating circuit 28 having as an element of control quartz crystal 30, which latter causesl a constant. frequency output to be sent into filter 3| for filtering out all extraneous and harmonic frequencies in order to produce a suitable pure and steady frequency of oscillating circuit 29. The output of the two oscillating circuits mix in .jdetector 32 and the resulting beat frequency, a function of barometer condenser 28, is sent out by means of a radio telephony transmitter 34, after amplication through amplifier' 33. 'Ihe regular transmitting equipment of an aircraft can be used for transmitting the beat frequency signals. t

The described equipment is applicable for othe purposes than measuring air pressuresor altitudes as for example for making remote gasoline oil or water tank measurements, remote electric meter indications etc. l

The block Idiagrams of Figures 3` and 4 illustrate simplified lay outs in which a head tele'- phone set replaces the detectors, amplifiers a'nd the frequency meter.A The switching arrangement of these lay outs permitsV more freedomrin the use of the equipment forv,the purpose desired. The sender station equipment shown is such as commonly used, for example, by an aircraft.

Thisequipment includes the Vordinary radio equipment of an aeroplane and a small The arrangement of parts and instruments will best be illustrated by describing the method of operation. Assuming that switch 31 is thrownto the left, the frequency of oscillating circuit 35, governed byeair pressure device 36 and oscillator 35 will then be audible in phone 42 vof head phone set 43. Receiving set 44 with its receiv-` ingv antenna 45 and ccuntrpoise 45' 4picks up the` frequency of the remote station, which frequency 'is proportional to the height of said station, and will-be heard in phone 46. Consequently the aviator cancompare the frequencies of the two notes in phones 42 and 46 and after little practice accuratelyl ,determine his altitude with respect to the remoteflstation. Turning of switch 38 upwardly connects the oscillating circuit 35 with vthe transmitting device so thatthe remote station can determine the altitude of the aircraft. When switches 3'I and 38 'are turned in reverse directions to that just described the oscil-V lating circuit is cut out and the operator may use his equipment for radio communication over microphone 41 and head phones 42 and 46.

The block diagram shown in Figure 4 reprel sents the equipment used at a ground station or led to double jacks 5| and 52 and to single jack 53, and theoutput frequency of oscillator 56 embodying calibrated condenserA 55 and oscillator 56, which frequency is a function of the` dial setting of condenser 55, is led to double jacks 5| and 51 and to single jack 58. `l'giinally the output of' receiving set 59, including antenna 68 and counterpoise 6|, is led Yto double jacks 51, 52 and 62. Microphone 63 is, connected to single jack 64, transmitting set 65 with antenna 66 andv coun- -terpoise 61 is'connected to a single telephone brated condenser 55 can be adjusted, by turning the condenser dial to zero and manipulating a zero adjusting condenser (not shown) until the tones in phones 69 and 18 are identical@ When double plug 12 is inserted into double jack 51 the output of receiving set 59 and the output' of oscillator 56 will be heard in the respective phones. In this position of plug 12`the dial of th calibrated condenser 55 is turned until the -notes in phones 69 and 18 are the sameso that the position of the dialof the calibrated condenser is al measure for the incoming frequency. The .dial of thecondenser'55 may of course be calibrated in pounds/bf pressure, inches of mercury, or feet of altitude.

When double plug 12 is inserted into double jack 62, the receiving set 59 is connected to both phones so that the receiver can be used for normal reception. Single plug 68, when inserted into jack-58, connects the transmitting set 65 with oscillating circuit 54, and when inserted into jack 53 connects transmitting set 65 with oscillating circuit 48. Finally `when plug 68. is inserted in jack 64 the microphone'63 is connectedwith the transmitting set for normal speech transmission. The transmission of the output of oscillating' circuit 54 to the remote station imparts the necessary lfrequency to permit the dial of the calibrated condenser of this station to be set to its correct position, and' the transmission of the output of the oscillating circuit 48 to said remote station permits the operator at the latter stationto make measurements or comparel his altitude with respect to the sender station; y

The wire diagram of Figure 5 is identical with the block diagram of Figure 3, adapted forI use on aircraft.' This diagraml inadditionto the-conventional equipment of an aeroplanealso includes a beat frequency oscillator and an'air pressure device, making the frequency of the oscillator a function of the air pressure.A Numerals 13 to 83 inclusive indicates thediff'erent parts of the beat frequency oscillator. Thus a quartz crystal 13 Y insures a constant frequency of oscillation o f the former 11. The output of an oscillator 18-is also fed through transformer 11 into the balanced modulator 16. The output of oscillator 18 is controlled by a variable condenser 19 across the secondary of transformer 11. Balanced modulator 16 is coupled with an amplifier 88 through a transformer 8| in such a way that a low pass filter action is insured. Finally the output of amplifier 88 is fedinto apower amplifier 82 and thence through an output transformer 83 into jacks 84 and 85.

The wiring -diagram of the transmitting set of Figure 5 diagram is-indicated by numerals 86 to inclusive. This transmitting set includes a master oscillator circuit 86, which feeds into the power amplifier circuit 81, where the radio frequency of the master oscillator circuit 86 is modulated in the plate circuit of the powerl amplifier before it is 'fed through relay 86 into the antenna 89. Direct current voltage is supplied from a motor generator 98 operating from the |2 volt storage battery 9| of the aeroplane. The frequency to be transmitted is fed from plug 92 through the input transformer 93 to vacuum tube 94, where it is amplified before being fedjnto modulator tube 95.

When 'relay 88 is in receiving position, the antenna is connected to the receiving set, indicated by'numeral 96 to |89 inclusive. This receiving set embodies three stages or tuned radio frequency amplification circuits 96 91 and 98, the regenerative detector 99, and two stages of audio frequency amplification |88 and |8I. The output of the receiving set is'fed .into jacks |82 and |83. A head phone set |84 with ear phones |85 and |86 is'connected to a. double plug |81 which may be plugged into double jack |82 or single jacks84 and |83, and a microphone |88 connected to a single jack |89 may be connected with plug 92 or the latter may be plugged into singlejack 85.I s the wiring diagram just described is identical with the block `diagram of Figure 3, the operation of which has vbeen fully described, further ,explanation is deemed unnecessary.

The Wire diagram of Figure 6 is identical with the block diagram of Figure 4, adapted for ground or receiving station usage. Figure 6 diagram is somewhat similar to the diagram shown in Figure 5 and includes in addition to the conventional radio station equipment, a beat frequency oscillator, an air pressure device-for making the frequency of the oscillator a.` function of the air pressure, and a second beat frequency oscillator controlled by a calibrated condenser.

' Numerals H8 to |28 inclusive indicate the different parts of the rst beat frequency oscillator.

output of an oscillator ||5 is also fed through transformer i I4 into the balanced modulator H3. 'The output of oscillator H5 is controlled by a variable condenser H8 across the'secondaryof transformery H4. Balanced modulator ||3 is coupled with an amplifier ||1 through a transformer ||8 in such away that a low passlter actiofnfis insured. Finally the output of amplifier I|1 is fed'into a. power amplifier H9 and thence through an output transformer |28 into jacks |2| and |22.

The wiring diagram of the transmitting set is ,l

indicated by numerals |23 to |32 inclusive. This transmitting 4set includes a master oscillator ciris filtered in filter cuit |23, which feeds into the power amplifier circuit |24, where the radio frequency of the master oscillator circuit |23 is modulated before it is fed through relay |25 into the antenna |26. The direct current voltage supply is secured from a motor generator |21 operating from a battery |28. The frequency to be transmitted is fed from plug |29 through the input transformer |30 to vvacuum tube |3l, vwhere it is amplified before being fed into modulator tubes |32.

The receiving circuit embodies three stages of tuned radio frequency amplification circuits |33, |34 and |35, a generative detector |36, and two stages of audio frequency amplification |31 and |36. The output of the receiving circuit is fed to jacks |39, |2| and jack |30, and the output of the beat frequency oscillator is fed to jacks |2|, |22 and |40.

The second beat frequency oscillator designated in part by numerals I4! to |52 inclusive, is quite similar to the beat frequency oscillator previously v described. The frequency of this second beat frequency oscillator is controlled by a calibrated condenser |4|, provided with a suitably gradu"4 ated dial so that direct readings can be had. A zero adjusting condenser |42, sh'unted with respect to the calibrated condenser |l| permits adjustment to zero beat as previously described. The quartz crystal |43 controls the frequency of the oscillating circuit |44, the .output of which |45 and then fed through transformer |46 into the balanced modulator |41. The output of the oscillator |48, controlled by calibrated condenser |41, is also fed into balanced modulator |41. The beat note of this modulator passes through transformer |49 and the low pass filter arrangement into amplifier |50 and |5i, before passing through the output transformer |53 and |40 can be connected to an earphone set including phones |55, |56 by means of a plug |51 and jacks |54, |22 and |56, the latter of which, being connected to a microphone |59 can be connected with the sender by means of plug |29.

The diagrams hereinbefore described include a barometer condenser adapted to make the fre- .quency of the signals a function of the air pressure. Such a barometer condenser, may consist of an evacuated chamber |60, having yielding opposite walls or diaphragms |6I, |62 insulated 'from each other by insulating-material |63' (see Figures 7, 8 and 9). These diaphragms centrally support rods |63 and |64 respectively, rod |64 being rigidly secured to a base plate |65, covered by a layer of insulating material |66, and rod |63, being yieldingly supported` by means of a knife bar |61 secured to said rod and resting on a spring |68, supported by an adjustable bracket |69. This bracket is made of insulating material and supported Aon adjusting screws |18, |1| and |12, which screws bear upon the insulating material |66 of base plate |65 and permit hori zontal and vertical adjustment of bracket |69 if desired. It will be seen that rod |63 being under constant outward tension or pull,- will prevent collapse of the diaphragms under the effect of 4air pressure' until the tension of spring |68 has been overcome. The two diaphragms form the Plate f a: condenser and are electrically'connected to binding posts |13, |14 mounted on the insulating material |66 of base plate |65.

y)It should be understood that any device the capacity of which changes under pressure variations may of course be used in the place of the described barometer condenser. Thus mechanical devices automatically actuated by pressure variations and coupled with variable capacities may be used with the same results. A diagrammatic view of such an arrangement is shown in Figure of the drawings. In this figure an aneroid barometerv |16 actuates a variable condenser |11 by means of a lever |18, pivotally secured to the frame |19 of the barometer and connectedat its opposite ends to the yieldable diaphragm-|80 of the aneroid barometer and the. movable blades |8| of variable condenser |11. It will be obvious that liquid barometers may be used with the same effect as aneroid barometers and possibly with greater efficiency in exact adjustment. Furthermore, changes of capacity by pressure variations may be obtained by using special vacuum tubes of the type disclosed in my copending application previously mentioned herein. The change of the capacity of these tubes is caused by changing the physical relationship of the electrodes, by deformation of one or more yielding diaphragms forming part of the wall of the tube, which diaphragms support the inner electrodes of the tube.

In Figures ll to 13 I have shown a preferred form of calibrated dial H2 for the calibrated condenser which varies the output frequency of the beat frequency oscillator. This dial preferably embodies a logarithmetic calibration to permit of substantially accurate readings where most desirable. Forexample, if the dial is calibrated in feet altitude, the readings for low altitudes will be very accurate although direct-readings may be made up to 10,000 feet. Dial |82 is pivotally mounted on a main shaft |83, connected to a variable rotary condenser (not shown) and heldin proper position with respect to the panel board |84 by means of collar |85. The frontend of shaft |83 carries a dial knob |86, securely fastened to said shaft by a set screw |81. Dial knob |86 provides for quick approximate adjustments while shaft |96 having a small knob |88 is used for Vernier adjustments. Shaft |98 is preferably pivotally extended through the bottom portion of -to dial |82, so that rotation of worm shaft |92 causes relative rotation of dial |82 and' knob |86 with respect to each other.

vIt will be seen from the foregoing that the pilot of an air craft can make height measurements with the equipment described while listening to directional signals. As there is no necessity for employing a special radio channel, the invention can be practiced with the present cross country route systems. My method or rating and comparing spatio-etemperal quantities is particularly applicable for vaircraft work to determine the height of aircrafts with respect to each other or to the ground and will also `be `of great help in landing the aircrafts on a mothership or on the ground. The method may also be used effectively for determining the height of an aeroplane flying through the mountains. For the latter purpose equipment such as shown in Figures 4 and 6, or the sender station thereof together with the pressure operated beat frequency oscillator, may be installed` on mountain peaks for continuously vtransmitting the necessary beat frequency so that claim is:

l. In a method of rating and comparing the' heights of the two spaced points by means of their an aviator may determine-his proper height with respect to the mountain peaks to be crossed. In such case the air pressure devices or pressure condensers on the sending and receiving station are subjected to substantially the same general air conditions due to the proximity of the stations with respect to each other and consequently the readings will be very accurate.

'I'he invention may also be employed to good advantage in making topographical maps, as it permits of accurate determination of elevations at the points in question. v

While I have described the principles of opera tion of my invention together with apparatus for practicing the invention, I wish it to be understood that the apparatus shown and described herein is merely illustrative and that I do not restrict my invention to any particular apparatus.

Having thus described my invention, what I atmospheric pressure differences, the steps of creating at one point at low beat frequency between two oscillating circuits having high frequencies, making one of thetwo oscillating circuits a function of the atmospheric pressure atv the said point creating a second low beat frequency at the other point and making this second frequency a function of the atmospheric pressure at the other point and comparing the low beat frequencies at the same time with each other.

2. In a method o f rating and comparing the heights of two spaced points by means of their l atmospheric pressure differences the .steps of.

creating at one point an audio beat frequency, between two oscillating circuits of radio freqeuncy, creating at the other point V,an audio beat frequency between two oscillating circuits of radio frequencies making the two audible beat frequencies a function of the respectivebarometric pressures of said points and rating the heights of said points with respect to each other and comparing the audible beat frequencies with each ot en 3. In'a method of rating and comparing the 'heights of two spaced pointsby means of their atmospheric pressure differences the steps of creating at one of said points an audio beat frequency between two oscillating circuits oscillating in radio frequency, making this audible beat frequency a function of the barometric pressure at/ .this point, rating the audio beat frequency by comto said irst point and comparing the two audible vbeat frequencies with each other.

4. In a method of rating and comparing the 'heights of two spaced points according to claim 3 the additional steps of bringing the two audible mospheric pressure differences, the steps of creating at one of said points an audio beat frequency between anoscillating circuit, the oscillations of which are a function' of the barometric pressure at this point and an oscillation circuit of a constant frequency, in rating the audio beat frequency with a second audio beat frequency by bringing the twoaudio beat frequencies to a zero beat, creating at the other of said points an audio beat frequency between two oscillating circuits, making the latter audio beat frequency a function of the air pressure at the other point, transmitting this latter audio frequency to said first point and comparing the latter audio beat frequencies at said point by bringing this frequency .to zero beat with the second audio beat frequency at this point.

6. In an apparatus for comparing and rating the heights of spaced points by means of their atmospheric pressure differences, an electric oscillator, an automatically variable condenser coupled with said oscillator having its plates separated by an airtight yielding chamber to change thel condenser capacity and frequency of said oscillator in accordance with atmospheric pressure variations, a receiving set adapted to pick -up electric waves sent from a distant point, the

frequency of which waves is a function of the atmospheric pressure at said distant point and moans to compare and rate the frequency of said` circuit and the frequency ofthe picked up electric waves at the same time with each other.

7. In an apparatus for comparing the heights of spaced points by means of their atmospheric pressure differences, an electric oscillating circuit, an automatically variable lcondenser within said circuit having its plates separated by an airtight yielding chamber to change the capacity of the condenser and the frequency of said oscillator in accordance with atmospheric pressure variations, a receiving set adapted to pick up electric waves sent from a distant point, the frequency of 4which waves is a function of the atmospheric pressure at said distant point and a telephone ear set having one phone coupled with said oscillating circuit and its other phone coupled with said receiving set to permit comparison of the frequency of said oscillator with the frequency of said incoming waves.

8. In an .apparatus for comparing the heights of spaced points by means of their atmospheric pressure differences, radio frequency oscillators coupled to produce an audio beat note, one of said 4oscillators including automatically variable condenser means having its plates separated by yielding air-tight chamber for changing the capacity of said condenser in accordance with atmospheric pressure variations so that the audio beat note is a function of the atmospheric pressure, a receiving set adapted to pick up an audio beat frequency sent from a remote point, which note is a function of the air pressure at said remote point, and a telephone ear sethaving one phone coupled with said beat note oscillator to reproduce the sound of said beat note'and its other phone to said receiving set to reproduce the sound of the beat note. received from said remote point.

'9. The combination of a send'erstation having an oscillator, automatically variable, pressure operated tuning means for changing the tuning of said oscillator in accordance with atmospheric pressure changes with an apparatus substantially remote from said sender station embodying a. receiving set for picking up the waves of said sender l station,`said apparatus including an oscillator, an

automatically variable -pressure operated .tuning means for changing the tuning of said latter oscillator-'in accordance with atmospheric pressure chang, and means coupled with said receiving set and the oscillator of said apparatus for comparing and rating the frequency of the incoming waves of said se'nder station with the frequency of said oscillator of said apparatus.

10. The combination of a sender station embodying a radio frequency oscillator, means whereby the frequency of said oscillator is controlled inV accordance with atmospheric pressureA changes, a second radio frequency oscillator of constant frequency and means for producing a beat note between the oscillations of said two oscillators, with an apparatus substantially remote from said sender station embodying a receiving set for picking up the beatnote of said sender station, a radio frequency oscillator, means whereby the frequency of said last oscillator is controlled in accordance with atmospheric pressure changes, a second radio frequency oscillator of constant frequency, means for producing a beat note between the oscillations of the two oscillators of said apparatus, and means coupled with said receiving set and the means producing a beat note in said apparatus for comparing and rating the beat note of said sender station with the beat note of said apparatus. v

111. The method of determining altitude between an elevation and a lower point of reference, which comprises generating high frequencyv Waves under control of barometric pressures at said elevation and at said point, respectively; coordinating said waves to produce a resultant beat whose frequency representsthe pressure differential of said elevation relative to said point of reference; and detecting and evaluating said beat frequency in terms of altitude.

12.- The method of determining the altitude of aircraft which vcomprises the step of generating a high frequency wave on the-craft; controlling the frequency of said wave in response to barometric pressure at the flight level of the craft; generating a second high frequency wave at ground level; controlling the frequency of said second wave in response to barometric pressure at said ground level; combining the two waves to produce a resultant beat frequency; and detecting and evaluating said beat frequency in terms of altitude.

13. Means for determining the altitude of airvcraft above a given ground level, comprising sources of high frequency energy carried by said craft and located at said ground level, respectively; means responsive to barometric pressure and associated with each source to control the frequency outputs thereof; circuit'means to coordinate the energy outputs of said sources to produce a beat frequency representing the pressure differential at the position of said craft relative to 'said ground level, said means including a variable capacity calibrated to v indicate altitucie of the craft in accordance with variationsv necessary to maintain zero beat note.

SAMUEL E. LEONARD, J R. 

